Abstract

Radio Occultation (RO) data using Global Positioning System (GPS) signals have the potential to deliver climate benchmark measurements, since they can be traced, at least in principle, to the international standard for the second. The special climate utility of RO data arises from their accuracy and long-term stability due to self- calibration. We developed a retrieval scheme at the Wegener Center, which is especially focused on minimizing potential bias of atmospheric parameters and on using background information (which is needed for high altitude initialization) in a transparent way. The German research satellite CHAMP (CHAllenging Minisatellite Payload for geoscientific research) provided the first opportunity to create RO based climatologies over more than 6 years. Overlap with data from the Taiwan/U.S. FORMOSAT-3/COSMIC (Formosa Satellite Mission 3/Constellation Observing System for Meteorology, Ionosphere and Climate, F3C) mission allows testing the consistency of climatologies derived from different satellites. We show initial results for monthly and seasonal zonal mean dry temperature climatologies. Our results indicate excellent agreement between RO climatologies from different F3C satellites as well as between data from different RO missions. After subtraction of the estimated respective sampling errors, altitude- and latitude-resolved seasonal dry temperature climatologies derived from two different F3C satellites in closely adjacent orbits agree to within < 0.1 K almost everywhere in the considered domain between 8 km and 30 km altitude. While there is still the possibility of common systematic errors, the results obtained so far show that RO data from different satellites can be indeed combined without need for inter- calibration.